IDO1 and cancer: Recently, 3-hydroxy-l-kynurenamine (3-HKA), a biogenic amine that is produced via a lateral branch of the IDO1 pathway in both DCs and endothelial cells during inflammatory conditions as well as by cancer cells, has been identified as a crucial player in inhibiting CD8+ T lymphocyte proliferation and naïve-to-effector T cell maturation by blocking the STAT1/NF-κΒ pathway [139].